Numerous valve actuators, and particularly valve actuators for heating/cooling valves, incorporate an electric motor as the primary power source to operably drive the valve between an open condition and a closed condition. A gear train amplifies and transfers the torque from the motor to the valve. More particularly, the valve actuator rotates a valve member or manipulates a fluid control device, typically a ball, between the open and closed conditions.
Some valve actuators incorporate a return spring coupled to the gear train to drive the gear train in the opposite direction and return the valve member to a predetermined position when power is removed from the motor. The return spring is stretched as the gear train is driven by the electric motor and stores potential energy until the electric motor is de-energized. When the motor is de-energized the return spring contracts and back drives the gear train returning the valve member to the desired predetermined position, e.g. an open position or a closed position.
For example, a normally closed configuration will be configured such that if power is lost, the return spring will back drive the gear train to a predetermined position in which the actuator closes the valve, through the use of the mechanical energy stored in the spring. Conversely, a normally open configuration will be configured such that if power is lost, the return spring will back drive the gear train to a predetermined position in which the actuator opens the valve, through the use of the mechanical energy stored in the spring.
Depending on the configuration of the valve, a valve actuator that operates in a clockwise direction or a valve actuator that operates in a counter-clockwise direction may be required.
The electric motor extends the return spring as it rotates the valve member within the valve. Under control of the electric motor, drive speed of the gear train is limited by the electric motor. However, once power to the electric motor is removed, the spring retracts and the gear train is back driven. In this situation, the spring return speed is limited only by the gear train and valve resistance. With limited to no resistance, the return speed can be come excessive and destroy the gear train when the gear train encounters or impacts a positive stop at the end of the rotation of the gear train. This is particularly true when the gear train is under the load of the return spring and is being accelerated by the return spring as the gear train impacts the positive stop.
The present invention is aimed at improvements with regard to such valve actuators and preventing uncontrolled and detrimental effects of back driving of the gear train when the electric motor of the valve actuator is de-energized.